1729. 求关注者的数量
# Write your MySQL query statement below
select
    user_id,
    count(*) as followers_count
from
    Followers
group by
    user_id
order by
    user_id

160. 相交链表
class Solution {
    public:
        ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) 
        {
            if(headA==NULL || headB==NULL)
            {
                return NULL;
            }
            int countA = 1;
            int countB = 1; 
    
            ListNode* HA = headA;
            ListNode* HB = headB;
            while(HA!=NULL)
            {
                countA++;
                HA=HA->next;
            }   
            while(HB!=NULL)
            {
                countB++;
                HB=HB->next;
            }
    
            HA=headA;
            HB=headB;
            int sub = abs(countA-countB);
            if(countA>countB)
            {
                while(sub--)
                {
                    HA=HA->next;
                }
            }
            else if(countA<=countB)
            {
                while(sub--)
                {
                    HB=HB->next;
                }
            }
    
            while(countA--)
            {
                if(HA==HB)
                {
                    return HA;
                }
                HA=HA->next;
                HB=HB->next;
            }
    
            return NULL;
        }
    };